feat: PhotoPrism M0 bring-up — compose stack, web client, sidecar, migrate

Replace the legacy mule-image backend with PhotoPrism plus a thin
SvelteKit client and a Node sidecar for endpoints PhotoPrism doesn't
expose (file rename), and add a two-phase migrator (metadata via PUT,
heaps → albums) for the existing Postgres library.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docker-compose.photoprism.podman.yml

@@ -0,0 +1,28 @@
+# Podman-rootless overlay for the PhotoPrism stack.
+#
+# Apply alongside the base compose file:
+#   podman-compose --env-file .env.photoprism \
+#     -f docker-compose.photoprism.yml \
+#     -f docker-compose.photoprism.podman.yml \
+#     up -d
+#
+# Adds the podman-specific bits that would break a vanilla docker compose run:
+#   - userns_mode: keep-id maps container UID to the invoking host UID, so
+#     PhotoPrism (running as PP_UID:PP_GID inside) can actually read the
+#     bind-mounted originals volume on the host (which is owned by the host
+#     user, not by uid 1000-in-the-container-namespace).
+#   - the explicit security_opt entries on the base file work in podman as-is.
+
+services:
+  # MariaDB writes to a named volume managed by podman; its in-container
+  # `mysql` user expects to own that volume. keep-id breaks this by mapping
+  # in-container UID 999 to a podman-subuid that doesn't own the volume,
+  # so let mariadb use the default userns mapping (root-in-namespace).
+  mariadb:
+    # No userns_mode override — use podman defaults.
+    init: true
+
+  # PhotoPrism does need keep-id, so its container UID maps back to the
+  # host UID that owns the bind-mounted originals/.
+  photoprism:
+    userns_mode: keep-id